initially my mobo didn't have PCI-E 1.1 support only 1.0 but after some bios update GPU-Z showed 1.1 with my (currently broken) 8600GT!

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There are ways to downgrade/roll back to previous BIOS check website for your motherboard
info and ways to roll back, mostly eg Intel Motherboards use recovery method, i don't know about yours, so check manufacturer website.